Marcin Ziołek | Adam Mickiewicz University in Poznań (original) (raw)
Papers by Marcin Ziołek
Journal of Inclusion Phenomena and Molecular Recognition in Chemistry, Mar 31, 2009
A photochromic symmetric Schiff base, N,N′-bis(salicylidene)-p-phenylenediamine has been studied ... more A photochromic symmetric Schiff base, N,N′-bis(salicylidene)-p-phenylenediamine has been studied by means of stationary spectroscopic absorption and emission techniques in the IR and UV-vis spectral range in heterogeneous environments: microporous and mesoporous molecular sieves and micellar systems. The intermolecular hydrogen bonds between the molecule studied and silanol groups in mesoporous material have led initially to the stabilization of the cis-keto tautomer and later to a very effective hydrolysis. Persisting two-step color changes have been found to occur after the UV irradiation of the molecule studied encapsulated in microporous and mesoporous molecular sieves.
Physical Chemistry Chemical Physics, 2014
A numerical study of optimal bandgaps of light absorbers in tandem solar cell configurations is p... more A numerical study of optimal bandgaps of light absorbers in tandem solar cell configurations is presented with the main focus on dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs).
Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2009
A photochromic symmetric Schiff base, N,N′-bis(salicylidene)-p-phenylenediamine has been studied ... more A photochromic symmetric Schiff base, N,N′-bis(salicylidene)-p-phenylenediamine has been studied by means of stationary spectroscopic absorption and emission techniques in the IR and UV-vis spectral range in heterogeneous environments: microporous and mesoporous molecular sieves and micellar systems. The intermolecular hydrogen bonds between the molecule studied and silanol groups in mesoporous material have led initially to the stabilization of the cis-keto tautomer and later to a very effective hydrolysis. Persisting two-step color changes have been found to occur after the UV irradiation of the molecule studied encapsulated in microporous and mesoporous molecular sieves.
The Journal of Physical Chemistry C, 2011
ABSTRACT We report on femtosecond to millisecond (fs-ms) studies of the interactions of an effici... more ABSTRACT We report on femtosecond to millisecond (fs-ms) studies of the interactions of an efficient triphenylamine organic dye (TPC1) for photovoltaics with titanium-doped high porous MCM-41 (TiMCM-41) silicate materials in half and complete dye-sensitized solar cells (DSSCs). Stationary UV–visible absorption results indicate a higher dye loading (3–5 times) per Ti atom in the TiMCM-41-based solar cells in comparison with those based on typical titania nanoparticles (NPs). However, the dye loading per Ti atom decreases with increasing the Ti doping, and the total dye content is still smaller in the TiMCM-41 solar cells than in the NP ones. Time-resolved emission studies showed that the average electron injection times (from TPC1 to the titania conduction band) are about 2.5 times longer for the TiMCM-41 solar cells (12 ps) than using the classical titania NP ones (4.5 ps). However, taking into account the slow internal deactivation of the dye in both materials, the yield of electron injection is >90%. Nanosecond to millisecond (ns-ms) flash photolysis studies of films show that the (back) electron recombination from titania to the dye cation is slower using TiMCM-41 than that in the titania NPs (19 μs vs 7 μs). Similar experiments for complete solar cells indicate faster dye regeneration due to the electrolyte in the TiMCM-41 than in the titania NP devices (3 μs vs 8 μs). Therefore, from the point of view of interfacial charge separation, the results indicate comparable or even better performance of the TiMCM-41 than the typical titania nanoparticle. However, the solar cell performance and the total efficiency are much lower in the TiMCM-41 than in the NP devices. Additionally, the values of short-circuit current per Ti atom are higher for the NP devices, despite the higher dye content per Ti atom in TiMCM-41 samples. This suggests a strong limitation in the electron transport process along the TiMCM-41 channels. Hence, despite the promising interfacial properties observed in fast and ultrafast time scales, this kind of material needs further modification in terms of improving the total dye loading and the conductivity, in order to be suitable for DSSCs.
The Journal of Physical Chemistry B, 2010
The relaxation dynamics of 5,10,15,20-tetrakis(4-hydroxyphenyl)-porphyrin (p-THPP) in tetrahydrof... more The relaxation dynamics of 5,10,15,20-tetrakis(4-hydroxyphenyl)-porphyrin (p-THPP) in tetrahydrofuran (THF) and encapsulated within the human serum albumin (HSA) protein in water solution was investigated. The protein environment affects the B→Q(y) and Q(x)→Q(y) transition dynamics (from 80 and 140-200 fs in THF to 50 and 100 fs in HSA, respectively) as well as the lifetime of the relaxed Q(x) state (9.1 vs 9.9 ns). The most prominent differences are observed in the relaxation dynamics in the hot Q(x) state in HSA, which includes the energy transfer to the protein in ∼1 ps and much slower solvent-assisted thermal equilibration component of about 20-30 ps.
Photochemical & Photobiological Sciences, 2012
In this study, we report on the effects of solvent viscosity and polarity on the photochromic sal... more In this study, we report on the effects of solvent viscosity and polarity on the photochromic salicylaldehyde azine (SAA) molecule by examining the steady-state and UV-visible absorption results in the time scale from nanoseconds to hours, in solution and in a polymer film. For the neutral structure, the viscosity strongly affects the lifetime of the photochromic (trans-keto) tautomer by suppressing the second order quenching process, and thus increasing the photochrome lifetimes in highly viscous solvents to 500 μs in polar triacetine, and to 65 μs in non-polar squalane. Trapping SAA in a non-polar polymer film (polyethylene) results in further elongation of the photochromic lifetime (700 μs) by one order of magnitude (with respect to that in squalane), due to the retardation of the intramolecular back-isomerization. Another species, living significantly longer and absorbing more in the UV comparing to the photochrome, was identified as the syn-enol tautomer. The lifetime of this tautomer, created in a competitive mechanism to the photochrome creation, is much longer in non-polar solvents (hundreds of minutes) than in polar ones (tens of minutes), opposite to the trend observed for the photochrome. For the SAA anion, the transient living on the ns-μs time scale can be exclusively assigned to the triplet state, which is not observed for the neutral form at room temperature.
J Phys Chem C, 2010
We report on studies of salicylaldehyde azine (SAA) dissolved in dichloromethane solution and wit... more We report on studies of salicylaldehyde azine (SAA) dissolved in dichloromethane solution and within the cages of the faujasite zeolite (NaX) using steady-state and femtosecond to nanosecond time-resolved spectroscopy. In solution, an excited-state intramolecular ...
Chemical Physics Letters, Oct 1, 2001
The Letter discusses the mechanism and dynamics of intra-and intermolecular electronic relaxation... more The Letter discusses the mechanism and dynamics of intra-and intermolecular electronic relaxation of the S 2 state of a xanthione molecule in acetonitrile, a quenching solvent, as well as the most important properties of the S 2 -exciplex formed upon the quenching process. Despite very ecient quenching of S 2 -XT and other thiones it has not been possible so far to observe the S 2 -exciplex. Therefore transient absorption system with 120 fs resolution was successfully applied for this purpose: the S 2 -exciplex was identi®ed for the ®rst time, its lifetime ($30 ps) and transient absorption spectrum were determined as well as the mechanism of its formation and decay. Moreover, the authors observed the presence of a very fast intramolecular electronic relaxation process S v>0 2 3 S 0 during S 2 -state deactivation which competes with intramolecular vibrational redistribution in the S 2 -state. Ó
The experimental set-up for time dependent transient absorption/gain measurements with femtosecon... more The experimental set-up for time dependent transient absorption/gain measurements with femtosecond time resolution is presented. Using pump-probe spectroscopy technique with femtosecond pulses from Ti:Sapphire laser system (Spectra Physics), the optical density of transient absorption and transient gain in the spectral range of 330-700 nm, time resolution of 120 fs, can be measured with the precision of up to 0.005. Knowing the real time resolution and "zero time" dispersion of the system from two-photon absorption measurements, we performed femto-and picosecond study of electronically excited DCM molecule in c-C 6 H 12 and MeOH solution. The emission decay of the DCM molecule in the locally excited singlet state, S 1 -LE, was measured with picosecond time resolution using TCSPC set-up (Time Correlated Single Photon Counting). The steadystate and time resolved measurements permitted the determination of the properties of this locally excited singlet S 1 -LE state and the pathways of its deactivation. ᭧
Dyes and Pigments, 2015
The photo behaviour of indoline dye D149 on different metal oxide nanoparticles in functioning so... more The photo behaviour of indoline dye D149 on different metal oxide nanoparticles in functioning solar cells is investigated by time-resolved studies in the time range from 100 fs to several ns. The cells are also characterized by standard photovoltaic measurements. The electron injection is found to occur on the time scales from <200 fs to several tens of ps. Locally excited (LE) and charge transfer (CT) excited states of the dye are identified to participate in the electron injection and dye deactivation mechanisms. The dependence of the ultrafast dynamics on the coadsorbent concentration and energy density of the pump pulse indicates the important role of excited state self-quenching. A decrease in the photocurrent of the cells upon aging (very fast for ZnO and slower for TiO 2 nanoparticles) is found to be correlated with the transient absorption kinetics, with a probable explanation suggested as electrolyte-induced dye rearrangement and aggregate formation.
Optics Communications, 2001
The in¯uence of the intersection angle between pump and probe beams on the temporal resolution in... more The in¯uence of the intersection angle between pump and probe beams on the temporal resolution in time-resolved pump±probe experiments was investigated. The calculations were performed for the Gaussian temporal shape of the pulses and for both, rectangular and Gaussian spatial energy distribution of the beams. The results were experimentally veri®ed in the transient absorption measurements with femtosecond resolution. Ó
Electron transfer in the reaction center of the purple photosynthetic bacterium Rb. sphaeroides R... more Electron transfer in the reaction center of the purple photosynthetic bacterium Rb. sphaeroides R-26 has been studied at room temperature by transient absorption spectroscopy with a time resolution of 120 fs. Measurements of absorption changes were performed in the range from 400 nm up to 680 nm, after excitation with a laser pulse of 80 fs duration within the absorption band of the bacteriochlorophyll at 800 nm. The excited state of the primary donor, characterized by the absorbance changes extending over the whole spectral range investigated, appeared within 120 fs and gave rise to the bleaching of the Q x absorption band of bacteriochlorophyll at 600 nm, increased further by electron transfer to bacteriopheophytin in ϳ3 ps. Photoreduction of the bacteriopheophytin acceptor detected at 546 nm and 670 nm proceeded with the same time constant. Multiphase absorbance changes were relatively the largest in the blue spectral range between 415 nm and 450 nm. Apart from the immediate absorbance increase due to excitation of the primary donor, another fast increasing phase was detected characterized by a wavelength dependent time constant-from ϳ5.5 ps at 415 nm to ϳ1.9 ps at 450 nm. Both the photooxidised primary donor and photoreduced bacteriopheophytin contributed to the amplitude of this phase. The electron transfer from the reduced bacteriopheophytin to a quinone acceptor was observed as a decrease in the intensity of the transient absorption bands at about 422 nm and at 670 nm, with disappearance of the bleaching at 546 nm and increase of the bleaching at 600 nm, all in ϳ200 ps.
The Journal of Physical Chemistry C, 2012
Femtosecond time-gated fluorescence and nanosecond flash photolysis studies of seven complete, re... more Femtosecond time-gated fluorescence and nanosecond flash photolysis studies of seven complete, real titania nanoparticle solar cells sensitized with an efficient organic dye (TH305) were performed in order to investigate the role of the electrolyte composition on the charge transfer dynamics. The electron injection rate constants were found to range from 0.4 to 3.5 ps −1 in iodide-based electrolyte, and they well correlate with the shift of the conduction band edge potential of titania. The lithium cation additives resulted in 2 times faster electron injection rate constant (3.55 ps −1 ) with respect to that when larger sodium cations were used (1.86 ps −1 ). However, in the presence of a pyridine derivative component in the electrolyte solution, the electron injection rate constant decreased several times (0.38 ps −1 for Li + and 0.54 ps −1 for Na + ), while the electron injection efficiency was found to be still very high, 96−100%. The dye regeneration by the redox couple under relatively low fluence of excitation beam (0.4 mJ/cm 2 giving about 4 electrons per titania nanoparticle) proceeds with an average rate constant of about 40 × 10 3 s −1 and efficiency close to 100%, independent of the electron composition. However, for a larger fluence (2 mJ/cm 2 ) excitation, a titania−dye electron recombination process competes with the dye regeneration and lowers the solar cell efficiency. The effect of self-quenching, high vibrational levels of the dye excited state, and the neat solvent on the electron injection process are also discussed. This study clearly shows that for TH350-based DSSCs the best performance is obtained using Li + and TBP as additives to the iodide electrolyte, giving the highest open circuit voltage and almost 100% efficiency of electron injection and dye regeneration.
The Journal of Physical Chemistry C, 2012
The Journal of Physical Chemistry C, 2014
Time-resolved laser spectroscopy studies of complete solar cells sensitized with a near-infrared ... more Time-resolved laser spectroscopy studies of complete solar cells sensitized with a near-infrared absorbing dye (HY103) and filled with different electrolytes are applied to explain their macroscopic parameters (efficiency and short-circuit current). Particular attention is paid to the effect of coadsorbent, size of cations in electrolyte (lithium vs guanidine ones), and addition of tert-butylpyridine. A complete deactivation scheme in the cell is revealed, and the rates of electron injection and all other processes are explored. For the most efficient electrolyte, the electron injection rate constants are 0.21 ps −1 from monomers and 0.07 ps −1 from H-aggregates. Moreover, two important and novel findings are revealed: energy transfer from the excited state of monomers to H-aggregates (with rate constants from 0.04 to 0.25 ps −1 ) and the decrease of internal conversion rate in HY103 attached to the nanoparticles (0.01 ps −1 ) with respect to that of free dye in solution (0.06 ps −1 ). Thus, our study gives more clues to better understand the photobehavior of dye-sensitized solar cells.
The Journal of Physical Chemistry C, 2011
We report on femto-to nanosecond emission studies of the interaction of an organic dye (TPC1) for... more We report on femto-to nanosecond emission studies of the interaction of an organic dye (TPC1) for solar cells, of (electron-donor)-(-spacer)-(electron-acceptor) structure, with different semiconductor particles and aluminium doped MCM-41 silicate mesoporous ...
Journal of Inclusion Phenomena and Molecular Recognition in Chemistry, Mar 31, 2009
A photochromic symmetric Schiff base, N,N′-bis(salicylidene)-p-phenylenediamine has been studied ... more A photochromic symmetric Schiff base, N,N′-bis(salicylidene)-p-phenylenediamine has been studied by means of stationary spectroscopic absorption and emission techniques in the IR and UV-vis spectral range in heterogeneous environments: microporous and mesoporous molecular sieves and micellar systems. The intermolecular hydrogen bonds between the molecule studied and silanol groups in mesoporous material have led initially to the stabilization of the cis-keto tautomer and later to a very effective hydrolysis. Persisting two-step color changes have been found to occur after the UV irradiation of the molecule studied encapsulated in microporous and mesoporous molecular sieves.
Physical Chemistry Chemical Physics, 2014
A numerical study of optimal bandgaps of light absorbers in tandem solar cell configurations is p... more A numerical study of optimal bandgaps of light absorbers in tandem solar cell configurations is presented with the main focus on dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs).
Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2009
A photochromic symmetric Schiff base, N,N′-bis(salicylidene)-p-phenylenediamine has been studied ... more A photochromic symmetric Schiff base, N,N′-bis(salicylidene)-p-phenylenediamine has been studied by means of stationary spectroscopic absorption and emission techniques in the IR and UV-vis spectral range in heterogeneous environments: microporous and mesoporous molecular sieves and micellar systems. The intermolecular hydrogen bonds between the molecule studied and silanol groups in mesoporous material have led initially to the stabilization of the cis-keto tautomer and later to a very effective hydrolysis. Persisting two-step color changes have been found to occur after the UV irradiation of the molecule studied encapsulated in microporous and mesoporous molecular sieves.
The Journal of Physical Chemistry C, 2011
ABSTRACT We report on femtosecond to millisecond (fs-ms) studies of the interactions of an effici... more ABSTRACT We report on femtosecond to millisecond (fs-ms) studies of the interactions of an efficient triphenylamine organic dye (TPC1) for photovoltaics with titanium-doped high porous MCM-41 (TiMCM-41) silicate materials in half and complete dye-sensitized solar cells (DSSCs). Stationary UV–visible absorption results indicate a higher dye loading (3–5 times) per Ti atom in the TiMCM-41-based solar cells in comparison with those based on typical titania nanoparticles (NPs). However, the dye loading per Ti atom decreases with increasing the Ti doping, and the total dye content is still smaller in the TiMCM-41 solar cells than in the NP ones. Time-resolved emission studies showed that the average electron injection times (from TPC1 to the titania conduction band) are about 2.5 times longer for the TiMCM-41 solar cells (12 ps) than using the classical titania NP ones (4.5 ps). However, taking into account the slow internal deactivation of the dye in both materials, the yield of electron injection is >90%. Nanosecond to millisecond (ns-ms) flash photolysis studies of films show that the (back) electron recombination from titania to the dye cation is slower using TiMCM-41 than that in the titania NPs (19 μs vs 7 μs). Similar experiments for complete solar cells indicate faster dye regeneration due to the electrolyte in the TiMCM-41 than in the titania NP devices (3 μs vs 8 μs). Therefore, from the point of view of interfacial charge separation, the results indicate comparable or even better performance of the TiMCM-41 than the typical titania nanoparticle. However, the solar cell performance and the total efficiency are much lower in the TiMCM-41 than in the NP devices. Additionally, the values of short-circuit current per Ti atom are higher for the NP devices, despite the higher dye content per Ti atom in TiMCM-41 samples. This suggests a strong limitation in the electron transport process along the TiMCM-41 channels. Hence, despite the promising interfacial properties observed in fast and ultrafast time scales, this kind of material needs further modification in terms of improving the total dye loading and the conductivity, in order to be suitable for DSSCs.
The Journal of Physical Chemistry B, 2010
The relaxation dynamics of 5,10,15,20-tetrakis(4-hydroxyphenyl)-porphyrin (p-THPP) in tetrahydrof... more The relaxation dynamics of 5,10,15,20-tetrakis(4-hydroxyphenyl)-porphyrin (p-THPP) in tetrahydrofuran (THF) and encapsulated within the human serum albumin (HSA) protein in water solution was investigated. The protein environment affects the B→Q(y) and Q(x)→Q(y) transition dynamics (from 80 and 140-200 fs in THF to 50 and 100 fs in HSA, respectively) as well as the lifetime of the relaxed Q(x) state (9.1 vs 9.9 ns). The most prominent differences are observed in the relaxation dynamics in the hot Q(x) state in HSA, which includes the energy transfer to the protein in ∼1 ps and much slower solvent-assisted thermal equilibration component of about 20-30 ps.
Photochemical & Photobiological Sciences, 2012
In this study, we report on the effects of solvent viscosity and polarity on the photochromic sal... more In this study, we report on the effects of solvent viscosity and polarity on the photochromic salicylaldehyde azine (SAA) molecule by examining the steady-state and UV-visible absorption results in the time scale from nanoseconds to hours, in solution and in a polymer film. For the neutral structure, the viscosity strongly affects the lifetime of the photochromic (trans-keto) tautomer by suppressing the second order quenching process, and thus increasing the photochrome lifetimes in highly viscous solvents to 500 μs in polar triacetine, and to 65 μs in non-polar squalane. Trapping SAA in a non-polar polymer film (polyethylene) results in further elongation of the photochromic lifetime (700 μs) by one order of magnitude (with respect to that in squalane), due to the retardation of the intramolecular back-isomerization. Another species, living significantly longer and absorbing more in the UV comparing to the photochrome, was identified as the syn-enol tautomer. The lifetime of this tautomer, created in a competitive mechanism to the photochrome creation, is much longer in non-polar solvents (hundreds of minutes) than in polar ones (tens of minutes), opposite to the trend observed for the photochrome. For the SAA anion, the transient living on the ns-μs time scale can be exclusively assigned to the triplet state, which is not observed for the neutral form at room temperature.
J Phys Chem C, 2010
We report on studies of salicylaldehyde azine (SAA) dissolved in dichloromethane solution and wit... more We report on studies of salicylaldehyde azine (SAA) dissolved in dichloromethane solution and within the cages of the faujasite zeolite (NaX) using steady-state and femtosecond to nanosecond time-resolved spectroscopy. In solution, an excited-state intramolecular ...
Chemical Physics Letters, Oct 1, 2001
The Letter discusses the mechanism and dynamics of intra-and intermolecular electronic relaxation... more The Letter discusses the mechanism and dynamics of intra-and intermolecular electronic relaxation of the S 2 state of a xanthione molecule in acetonitrile, a quenching solvent, as well as the most important properties of the S 2 -exciplex formed upon the quenching process. Despite very ecient quenching of S 2 -XT and other thiones it has not been possible so far to observe the S 2 -exciplex. Therefore transient absorption system with 120 fs resolution was successfully applied for this purpose: the S 2 -exciplex was identi®ed for the ®rst time, its lifetime ($30 ps) and transient absorption spectrum were determined as well as the mechanism of its formation and decay. Moreover, the authors observed the presence of a very fast intramolecular electronic relaxation process S v>0 2 3 S 0 during S 2 -state deactivation which competes with intramolecular vibrational redistribution in the S 2 -state. Ó
The experimental set-up for time dependent transient absorption/gain measurements with femtosecon... more The experimental set-up for time dependent transient absorption/gain measurements with femtosecond time resolution is presented. Using pump-probe spectroscopy technique with femtosecond pulses from Ti:Sapphire laser system (Spectra Physics), the optical density of transient absorption and transient gain in the spectral range of 330-700 nm, time resolution of 120 fs, can be measured with the precision of up to 0.005. Knowing the real time resolution and "zero time" dispersion of the system from two-photon absorption measurements, we performed femto-and picosecond study of electronically excited DCM molecule in c-C 6 H 12 and MeOH solution. The emission decay of the DCM molecule in the locally excited singlet state, S 1 -LE, was measured with picosecond time resolution using TCSPC set-up (Time Correlated Single Photon Counting). The steadystate and time resolved measurements permitted the determination of the properties of this locally excited singlet S 1 -LE state and the pathways of its deactivation. ᭧
Dyes and Pigments, 2015
The photo behaviour of indoline dye D149 on different metal oxide nanoparticles in functioning so... more The photo behaviour of indoline dye D149 on different metal oxide nanoparticles in functioning solar cells is investigated by time-resolved studies in the time range from 100 fs to several ns. The cells are also characterized by standard photovoltaic measurements. The electron injection is found to occur on the time scales from <200 fs to several tens of ps. Locally excited (LE) and charge transfer (CT) excited states of the dye are identified to participate in the electron injection and dye deactivation mechanisms. The dependence of the ultrafast dynamics on the coadsorbent concentration and energy density of the pump pulse indicates the important role of excited state self-quenching. A decrease in the photocurrent of the cells upon aging (very fast for ZnO and slower for TiO 2 nanoparticles) is found to be correlated with the transient absorption kinetics, with a probable explanation suggested as electrolyte-induced dye rearrangement and aggregate formation.
Optics Communications, 2001
The in¯uence of the intersection angle between pump and probe beams on the temporal resolution in... more The in¯uence of the intersection angle between pump and probe beams on the temporal resolution in time-resolved pump±probe experiments was investigated. The calculations were performed for the Gaussian temporal shape of the pulses and for both, rectangular and Gaussian spatial energy distribution of the beams. The results were experimentally veri®ed in the transient absorption measurements with femtosecond resolution. Ó
Electron transfer in the reaction center of the purple photosynthetic bacterium Rb. sphaeroides R... more Electron transfer in the reaction center of the purple photosynthetic bacterium Rb. sphaeroides R-26 has been studied at room temperature by transient absorption spectroscopy with a time resolution of 120 fs. Measurements of absorption changes were performed in the range from 400 nm up to 680 nm, after excitation with a laser pulse of 80 fs duration within the absorption band of the bacteriochlorophyll at 800 nm. The excited state of the primary donor, characterized by the absorbance changes extending over the whole spectral range investigated, appeared within 120 fs and gave rise to the bleaching of the Q x absorption band of bacteriochlorophyll at 600 nm, increased further by electron transfer to bacteriopheophytin in ϳ3 ps. Photoreduction of the bacteriopheophytin acceptor detected at 546 nm and 670 nm proceeded with the same time constant. Multiphase absorbance changes were relatively the largest in the blue spectral range between 415 nm and 450 nm. Apart from the immediate absorbance increase due to excitation of the primary donor, another fast increasing phase was detected characterized by a wavelength dependent time constant-from ϳ5.5 ps at 415 nm to ϳ1.9 ps at 450 nm. Both the photooxidised primary donor and photoreduced bacteriopheophytin contributed to the amplitude of this phase. The electron transfer from the reduced bacteriopheophytin to a quinone acceptor was observed as a decrease in the intensity of the transient absorption bands at about 422 nm and at 670 nm, with disappearance of the bleaching at 546 nm and increase of the bleaching at 600 nm, all in ϳ200 ps.
The Journal of Physical Chemistry C, 2012
Femtosecond time-gated fluorescence and nanosecond flash photolysis studies of seven complete, re... more Femtosecond time-gated fluorescence and nanosecond flash photolysis studies of seven complete, real titania nanoparticle solar cells sensitized with an efficient organic dye (TH305) were performed in order to investigate the role of the electrolyte composition on the charge transfer dynamics. The electron injection rate constants were found to range from 0.4 to 3.5 ps −1 in iodide-based electrolyte, and they well correlate with the shift of the conduction band edge potential of titania. The lithium cation additives resulted in 2 times faster electron injection rate constant (3.55 ps −1 ) with respect to that when larger sodium cations were used (1.86 ps −1 ). However, in the presence of a pyridine derivative component in the electrolyte solution, the electron injection rate constant decreased several times (0.38 ps −1 for Li + and 0.54 ps −1 for Na + ), while the electron injection efficiency was found to be still very high, 96−100%. The dye regeneration by the redox couple under relatively low fluence of excitation beam (0.4 mJ/cm 2 giving about 4 electrons per titania nanoparticle) proceeds with an average rate constant of about 40 × 10 3 s −1 and efficiency close to 100%, independent of the electron composition. However, for a larger fluence (2 mJ/cm 2 ) excitation, a titania−dye electron recombination process competes with the dye regeneration and lowers the solar cell efficiency. The effect of self-quenching, high vibrational levels of the dye excited state, and the neat solvent on the electron injection process are also discussed. This study clearly shows that for TH350-based DSSCs the best performance is obtained using Li + and TBP as additives to the iodide electrolyte, giving the highest open circuit voltage and almost 100% efficiency of electron injection and dye regeneration.
The Journal of Physical Chemistry C, 2012
The Journal of Physical Chemistry C, 2014
Time-resolved laser spectroscopy studies of complete solar cells sensitized with a near-infrared ... more Time-resolved laser spectroscopy studies of complete solar cells sensitized with a near-infrared absorbing dye (HY103) and filled with different electrolytes are applied to explain their macroscopic parameters (efficiency and short-circuit current). Particular attention is paid to the effect of coadsorbent, size of cations in electrolyte (lithium vs guanidine ones), and addition of tert-butylpyridine. A complete deactivation scheme in the cell is revealed, and the rates of electron injection and all other processes are explored. For the most efficient electrolyte, the electron injection rate constants are 0.21 ps −1 from monomers and 0.07 ps −1 from H-aggregates. Moreover, two important and novel findings are revealed: energy transfer from the excited state of monomers to H-aggregates (with rate constants from 0.04 to 0.25 ps −1 ) and the decrease of internal conversion rate in HY103 attached to the nanoparticles (0.01 ps −1 ) with respect to that of free dye in solution (0.06 ps −1 ). Thus, our study gives more clues to better understand the photobehavior of dye-sensitized solar cells.
The Journal of Physical Chemistry C, 2011
We report on femto-to nanosecond emission studies of the interaction of an organic dye (TPC1) for... more We report on femto-to nanosecond emission studies of the interaction of an organic dye (TPC1) for solar cells, of (electron-donor)-(-spacer)-(electron-acceptor) structure, with different semiconductor particles and aluminium doped MCM-41 silicate mesoporous ...